Machine for cutting screw threads



July 3, 1934.

H. GODZIEWSKI IACHINB FOR CUTTING SCREW THREADS I Filed Sept. L 1, 19:3

fl? renfax Patented July 3, 1934 UNITED STATES MACHINE FOR CUTTING SCREW THREADS Hermann Godziewski, Eichwalde, near Teltow, Germany Application September 1, 1933, Serial No. 687,884 In Germany September 16, 1932 Claims.

The invention relates to-machines for cutting screw threads, which operate during forward and backward feed. In such machines it is known to compensate for the play, arising upon the return 5 movement of the cooperating parts of the driving mechanism, in such a way'that the work carrier is arranged to be movable within limits between adjustable stops provided on a driver member.

This device has, however, exhibited various defects. It is only suitable within very restricted limits, if the play in the apparatus corresponds to less than one complete rotation of the work. Further the construction thereof becomes very complicated and diflicult when the apparatus is to be used for cutting internal screw threads. Another disadvantage of this device is that it can only be exactly adjusted when the machine is stationary.

The object of the present invention is to remove these defects, and in accordance with the invention compensation for the play between the cooperating parts of the'driving mechanism is now effected by introducing such a predetermined amount of artificial play in an axial bearing of the guide-spindle which transmits the 1ongitudinal movement to the work or work-support,

that upon reversal of the driving mechanism the longitudinal movement of the work or work-support is delayed until the work, taking into account the inherent lost motion of the driving mechanism, has made one or more complete revolutions. i

For this purpose in accordance with a pre ferred embodiment of the invention, the guidespindle is provided at one end with a bearing washer adapted to abut against a counter-washer which is arranged to be adjustable in the axial direction of the guide spindle, and the adjustment of this counter washer, i. e. the regulation of the artificial play, is arranged to be efiected by hand during operation of the apparatus;

In order that the invention may be readily understood it will now be described, by way of example, with reference to the accompanying drawing, in which Figure 1 is a view in longitudinal section of a screw thread cutting apparatus embodying the invention,

Figure 2 being a detail view also in longitudinal section on a larger scale, showing the counter washer in a position of adjustment.

Referring now to the drawing, the work-support 1 is mounted on a bed-plate 2 in a known manner. The work 3, for instance an internally screw-threaded caliper ring is secured in a centering plate 4 located on a shaft 5, the latter being arranged to be rotated bya driving disc 6, through the intermediary of reversible gearing 7, and to rotate the guide spindle 11 through the intermediary of toothed gearing 8, 9, 10. The toothed wheel 10 transmits its rotary motion to the guide spindle over a hollow shaft 10', to which the guide spindle is so connected as to permit longitudinal movement with respect thereto. For transmitting longitudinal movement to the support 1 the guide spindle cooperates with a nut member 12 secured to the bed-plate 2, and is provided at its free end with a bearing washer 13. This washer 13 is adapted to abut against a fixed counter washer 14 rigidly connected to the support 1, or against a counter washer 15 which is adjustable in the axial direction of the guide spindle, according to the direction of the longitudinal movement imparted to the support 1 by the guide spindle 11. The washer 15 has a screw-thread extended portion 15 which cooperates with a correspondingly screw-threaded portion of the support 1 and with a worm wheel rotatably secured to the support 1 and adapted to be operated by means of a worm 17. The thread-cutting device is here illustrated diagrammatically at A, as device for cutting internal screw-threads. The operation of the apparatus is as follows:

Whilst the apparatus is at rest prior toa cutting operation, the amount of play in the driving mechanism is determined exactly. In order to do this, the washer 15 is adjusted until it abuts against the washer 13, so that the guide spindle 11, disregarding the play between the latter and the nut-member 12, is operatively connected for axial movement with the support 1. Then the shaft 5 with the centering disc 4 and work 3 is turned to and fro by hand, it being observed upon the. reversal of movement how many partial or complete revolutions are made by the work before its longitudinal movement is initiated by the guide-spindle. This amount is the play, which may, for instance, be found to be 0.8 revolutions of the work.

A threadcutting operation is now efiected in the forward direction (to the left in Figure 1), the cutting disc preferably being permitted to run out of the last thread so as to be out of engagement with the work. At this stage the washer 13 is abutting against the washer 14.

In order, when the thread is to be cut during movement of the work in the opposite direction, to bring the cutting disc back to the same position with respect to the work as in the Ior-- 110 ward movement, which condition is essential for perfect formation of the screw-thread, the play must be compensated for, that is, the commencement of the rotary movement of the work upon reversal of the driving mechanism must agree exactly with the commencement of its longitudinal movement. In order, in the present example, to prevent the longitudinal movement of the work commencing after the latter has made 0.8 revolutions, which is equivalent to a movement of the cutting disc relative to the work, an amount a:, (Figure 2) of axial play is given to the guide spindle by adjusting the washer 15 through the intermediary of the worm gearing 16, 17. The value of a: is such that the work must have made exactly one revolution when the washer 13 abuts against the counter washer 15 and causes the longitudinal movement of the support 1 and the work to commence. If again the inherent play in the driving mechanism is equivalent to 1.4 revolutions of the work, a: will be so chosen that the work will make exactly two complete revolutions before its longitudinal movement commences. It is merely a matter, therefore of always enlarging the play to a number of complete revolutions, so that the work returns to its original position relative to the cutting disc without longitudinal movement. This longitudinal movement will consequently be imparted to the work by the guidespindle after the-work has made one or more revolutions, in which the inherent play in the driving mechanism is included, and upon each reversal of the driving mechanisnrthe rotary and longitudinal movements of the work will be in absolute agreement.

I claim:

1. The method of compensating the inherent lost motion in screw cutting machines wherein the work is revolved and is fed longitudinally by a feed screw, which method consists in increasing the inherent lost motion by an amount of lost motion sufiicient to bring the total lost motion to that corresponding to revolution of the work through a multiple of 360.

2. In screw cutting machines having a carriage supporting a revolving work holder and 9.

feed screw for feeding the carriage longitudinally,'a/lost motion compensating device including a loose connection between the feed screw and carriage permitting limited movement of the screw longitudinally of the carriage, and means for adjusting the extent of said limited movement.

3. In screw cutting machines having a carriage supporting a revolving work holder and a feed screw for feeding said carriage longitudinally, a lost motion compensating device including a collar on said feed screw, 2. pair of thrust bearings for the shaft supported by the carriage on opposite sides of said collar, one of said bearings being mounted for movement along the shaft toward and from the other bearing, and means to adjust the position of the movable bearing.

4. In screw cutting machines having a carriage supporting a revolving work holder and a feed screw for feeding said carriage longitudinally, a lost motion compensating device including a collar on said feed screw, a pair of thrust bearings for the shaft supported by the carriage on opposite sides of said collar, one of said bearings being mounted'for movement along the shaft toward and from the other bearing, a screw threaded extension on the movable bearing, a nut on the carriage through which said extension is screwed, and means to rotate the movable bearing in its nut whereby to adjust its position relative to the remaining bearing.

5. In screw cutting -machines having a carriage supporting a revolving work holder and a feed screw for feeding said carriage longitudinally, a lost motion compensating device includinga collar on said feed screw, a pair of thrust bearings for the shaft supported by the carriage on opposite sides of said collar, one of said bearings being mounted for movement along the shaft toward and from the other bearing, a screw threaded extension on the movable bearing, a nut on the carriage through which the said extension is screwed, a worm wheel fixed on said extension, and a manually operable worm meshing with said worm wheel.

HERMANN GODZIEW SKI. 

